Small voltage interrupter



2 1948- M. D. LISTON ET AL SMALL VOLTAGE INTERRUPTER Filed Sept. 14, 1945 Juventow Patented May25, 1948 SMALL VOLTAGE INTERRUPTER Max D. Liston and Clark E. Quinn, Detroit, Mich,

minors to General Motors Corporation, Detroit, Micla, a corporation of Delaware Application September 14, 1945, Serial No. 616,168

Claims. (Cl. 200-27) ilar current transforming problems arise with ultra small or micro currents such as those available from thermocouples, then the construction of the circuit interrupters or breakers becomes.

important inasmuch as any small errors may easily be greater than the current actually being measured. Therefore, in the construction of a breaker for an amplifier for thermocouple currents many problems arise, some of which may be briefly mentioned as follows: Any ambient temperature changes in the vicinity of the breaker may cause thermal currents of greater value than the current flow due to the thermocouple; contact resistance changes, or frictional engagement of the same causing temperature changes may cause like errors and thermo-electric properties of the different materials may also introduce errors.

It is therefore an object of our invention to provide circuit breaking means for interrupting ultra small currents in which substantially no contact thermal changes are present.

It is a further object of our invention to provide circuit breaking means in which a minimum of thermo-electric stray currents are found.

It is a still further object of our invention to provide a circuit interrupter for interrupting ultra small currents in which any stray currents attributable to contact resistance variation, thermo-electric currents or variation in ambient temperature are substantially eliminated.

With these and other object in view which will become apparent as the specification proceeds, our invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawings, in

which: v

Figure l is an end view, parts being broken away and shown in section, of one of our current interrupter units;

Figure 2 is a side view of a pair of interrupters used in a breaker amplifier; and

Figure 3 is a circuit diagram showing the con- 2 nections of a portion of the breaker amplifier circuit utilizing the breaker shown in Figure 1.

Referring now more specifically to the drawings and that form of invention shown in Figures 1 and 2, there is shown a pair of spaced supporting plates 2-4 which carry identical interrupter means and which are connected together by flanged sleeve 6 which rotatably supports a shaft 8 driven by a pulley Iii. As will be evident if direct current is to be interrupted to form alternating current for the purpose of transforming the same to a higher voltage and then amplified and again interrupted or rectified to provide a higher useable direct current, it will be necessary to synchronize the interruptions in the input circuit to the amplifier and those in the output therefor. For this purpose there is provided the two synchronized interrupters as shown in Figure 2 driven by a common shaft 8. On this shaft 8 are therefore provided two identical cams l2 and i4 producing the mechanical movement for the breaker arms.

Since the breakers are identical, only one will be described in detail. These breakers, as shown in Figures 1 and 2, consist of a follower l6 which is adapted to engage the exterior surface of cam I-4 and is supported on the outer end of a pivoted substantially mechanical rigid arm l8 rotatably supported on a pin 20 carried by the backing plate 2. This arm has secured to its opposite end a. transverse member 2| formed of insulating material such as fiber and which engages the extending ends of a pair of spaced arms 22 and 2-4 which latter carry the actual breaker contact points 26 and 28. The lower ends of the arms 22 and 24 are pivotally supported by small pins 30 and .32 which are adapted to ride on tapered surfaces 34 of a stationary insulating member and are secured in this position by short leaf springs '36 and 38, these springs being likewise secured to the insulating member or block 40. This block also carries two longer and extended spring members 42 and 44 which engage the arms 22 and 24 substantially mid-way of their length and opposite the electrical contacts and tend to bias them toward each other and the actuator 2| and are non-resonant at the frequencies used.

Supporting block 40 also carries the cooperating stationary contacts '46 and 48 which cooperate with the movable contacts 26 and 28 to form the circuit interrupting means. The pivotal arm I8 is spring biased toward the cam surface by a loop spring 50 having one end thereof riveted to the arm and the other remote end secured 3 to the backing plate 2. The stationary contacts 46 and 48 are adjustably secured to the support 40 and locked in-position by suitable set screws 52. The electrical connections to the stationary contacts 46 and 48 are made directly thereto through soldering the lines in slots such as 49v provided for that purpose. The movable contacts 26 and 28 are connected back to terminal strips 5| and 53 through conductive lines 55 and 51. Thus as the cam l4 revolves its contour will force the follower l6 to different radial distances causing rotation of the arm i8 about its pivot 20 and therefore relative movement between the stationary contacts 46 and 48 and the movable contacts 26 and 28 and the alternate opening and closing of the switches formed thereby,

In dealing with minute voltages and currents of the order of those contemplated in this instance, certain factors must be considered which do not have to be dealt with normally. Any stray current or noise in this amplifier input system is likely to introduce effects to make the amplifier output unintelligible. One such effect is that known as the Johnson noise or random motion of the electrons in a given circuit. Normally such an effect would introduce noise or errors so far below the level of the signals being studied that they do not have to be considered. But as the signals approach the same magnitude as the noise or errors then all precaution must be taken to keep the latter to a minimum.

To do this it is necessary to keep the impedance of the input circuit as low as possible for the reason that the noise from such sources is proportional to the absolute temperature and the square root of the resistance. The imped ance being a resistance factor must be kept down to as low a value as possible, and therefore any open circuit condition of this circuit must be avoided.

The device therefore is so designed that one set of contacts closes before the other set opens. In other words, there is an overlap in the operating cycle where both sets of conacts are closed, and therefore there is never a time when the circuit in which the contacts are connected is open. As shown in Figure l, the length of the operating bar 21 is provided to be slightly less than the distance between the outer faces of the contacts 46 and 48, so that in its intermediate position both switches are closed. A slight movement to the left of arm 24 caused by pressure from operating bar 21 and cam I4 will permit the contact 26 to move away from contact 46, and at the same time the right-hand end of arm 2| will leave the upper end of arm 22. Reverse movement of the operating arm 2| will permit closure of switch 26-46 "before switch 28-48 opens in the same manner.

'I'hecontacts 26, 28, 46 and 48 are made of pure gold inasmuch as this material has very little variation in the contact resistance through oxidation, and also very low thermo-electric potentials when associated with copper. Likewise, since the arms I 8, 22 and 24 are mechanically rigid and permit no bending, there will be no sliding of the movable contacts over the surface of the stationary ones, and therefore no friction in this engagement and no thermal changes due to said friction in the contacts. The engagement will be along a line axially of the contacts with no component at right angles thereto. In this manner we avoid contact resistance changes and also any error due to friction heat. A casing 54 lined with heat insulating material 56 surrounding the breaker points and arms 22 and 24 is provided to shield the breakers from stray electromagnetic and electro-- static fields.

All these precautions are necessary in view of the fact, as previously mentioned, that the currents which are being interrupted are minute and unless these precautions are taken, err0neouscurrents could easily be introduced having more amplitude than those currents which it is desired to interruptand amplify. Thus, as the follower I6 is moved radially of the cam by its motion contacts 26-46 are opened and closed in synchronization with contacts 28-48. The construction of the associated synchronized breaker indicated generally at 58 on the other supporting base 4 and driven by cam I2 is exactly the same as that just described and is as before mentioned used in the amplifier output to rectify the amplified current back to direct current for any desired use.

The electrical circuit into which this breaker is connected is shown generally in Figure 3 and consists of a pair of input lines 60 and 62 which are connected to some remote source such, for example, as thermocouples. Line 60 is connected to stationary contact 46 and the movable contact 26 associated therewith is connected by line 64 to one side of a primary Winding 66 of an input transformer for the amplifien. Line 62 is directly connected to the central tap on this same primary. The opposite terminal of the primary is connected through line 68 to movable contact 28, the stationary cooperating contact 48 of which is also electrically connected to input line 60. Thus, the input signal or current due to the thermocouple is alternately applied to the separate halves of the primary which induces alternating current in the secondary 10 which is connected to an amplifier (not shown).

We claim:

1. In current interrupter means, a base. an insulating block on said base, a plurality of electrical contacts mounted on said block, a plurality of movable arms mounted on said base, a second series of contacts mounted on said movable arms to engage the first-named contacts and form switching means therewith, the motion of the second-named contacts on said arms being purely axial of the first-named contact means so that no relative motion in the plane of the contacting surfaces occurs after contact is made, means for moving said movable arms so that one set of contacts closes before a second set opens to prevent the circuit controlled thereby from being entirely open at any time, said contacts being made of noble metal having low thermo-potential to copper.

2. In current interrupting means, a base, an insulating block on said base, a plurality of electrical contacts adjustably carried on said block, a plurality of mechanically rigid arms pivotally mounted on said block, cooperating contacts mounted on said arms to form switching means with the first-named contacts, spring biasing means to bias the arms toward the stationary contacts, a common cam-operated actuator engageable with both arms designed to actuate the arms so that one set of contacts must close before the other set opens and the circuit controlled thereby will never b fully open circuit.

3. In current interrupting means, a base, an insulating block on said base, a plurality of electrical contacts adjustably carried on said block, a plurality of mechanically rigid arms pivotally mounted on said block, cooperating contacts mounted on said arms to form switching means with the first-named contacts, spring biasing means to bias the anus toward the stationary contacts, a common cam-operated actuator engageable with both arms designed to actuate the arms so that one set of contacts must close before the other set opens and the circuit controlled thereby will never be fully open circuit, and the period during which both sets of contacts are closed may be varied by adjusting the stationary contacts.

4. In current interrupting means, an insulating support having oppositely disposed tapered surfaces thereon, a pair of contacts carried by said support, a pair of mechanically rigid arms carrying ivot pins bearing against said tapered surfaces on said support, spring means to maintain said pins in contact with said surfaces, contacts carried by said arms to cooperate with the firstnamed contacts, and a common cam-operated actuating member engageable with said arms to cause relative motion or the engaging contacts.

5. In current interrupting means, a base, an insulating block on said base, a plurality of electrical contacts carried on said block, a plurality of mechanically rigid arms pivotally mounted on said block, cooperating contacts mounted on said arms to form switching means with the firstnamed contacts, spring biasing means to bias the arms toward the stationary contacts and separate pivotal cam-operated actuator means formed at least in part of material resistant to heat transfer for said arms to avoid cam frictional heat flow to the contacts.

MAX D. LISTON.

CLARK E. QUINN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,105,399 Cadeli July 28, 1914 1,905,096 Irgens Apr, 25, 1933 2,007,338 Mallory July 9, 1935 2,166,901 Coiiey July 18, 1939 2,173,828 Doran Sept. 26, 1939 2,220,003 Schweizer Oct. 29, 1940 

